Recently, it has been reported that by administering flu vaccine targeting at an upper layer part of skin where many immunocompetent cells are present, even if the dosage is reduced, the same immunity acquisition ability as in subcutaneous administration or intramuscular administration can be obtained. Thus, by administering flu vaccine to the skin upper layer part, it is possible to reduce the dosage, so that there is a possibility that flu vaccine can be administered to more people. Note that the skin upper layer part refers to the epidermis and dermis of skin.
As the method of administering a drug to the skin upper layer part, methods using a single-needle, a multi-needle, a patch, gas, etc. are known. And, if stability and reliability of administration and production cost are considered, the method using a single needle is regarded most suitable for the method of administering a drug to the skin upper layer part. As the method of administering vaccine to the skin upper layer part using a single needle, a Mantoux method has been known from a long time ago. The Mantoux method is a method in which a needle, having generally 26-27 gauge in size and having a short bevel needle tip, is inserted into skin about 2-5 mm, from an oblique direction of about 10-15° relative to the skin, to administer a drug of about 100 μL.
However, the Mantoux method is difficult in manipulation, and the rate of success is left in the skill of the doctor giving an injection. In particular, a child has a possibility of moving at the time of administration, so that it is difficult to administer flu vaccine with the Mantoux method. Accordingly, it is desired that a device is developed that can administer vaccine to the skin upper layer part in a simple and convenient manner.
Patent Document 1 describes an injection device in which a limiter having a skin-contacting surface is connected with a needle hub mounted on a syringe. The limiter of the injection device described in Patent Document 1 is formed in a tube-like shape surrounding a needle tube, and has the skin-contacting surface from which an injection needle protrudes. The limiter regulates the length (protrusion length) of the injection needle protruding from the skin-contacting surface to 0.5-3.0 mm, and is adapted so that the drug injected from the injection needle is administered in the skin.
Patent Document 2 describes technique relating to a sticking adjustment tool for an injection needle that prevents an injection needle from being stuck deeper than a target depth and an injection needle assembly having the sticking adjustment tool. Sticking adjustment tools for an injection needle disclosed in Patent Document 2 include the one that is closely attached around an injection needle and has a skin-contacting surface.
Sometimes an injection device is used with suctioning a drug from a vial. The vial is a drug storage container capable of storing a drug for long periods in a liquid or freeze-dried state. The opening of the vial is sealed with a rubber stopper generally having the thickness of about 3-5 mm. The rubber stopper is made so as not to leak the drug even if the needle tube is stuck a plurality of times. Therefore, the majority of vaccine that is often vaccinated in a group setting is used by being suctioned from the vial.
The limiter described in Patent Document 1 and the sticking adjustment tool for an injection needle described in Patent Document 2 are configured to make the protrusion length of an injection needle relatively short (for example, 0.5-3.0 mm) so that the drug can be administered to the skin upper layer part. Therefore, it has led to that the injection needle cannot penetrate through the rubber stopper of a vial, and it has been impossible to suction the drug from the vial.
For example, if it is before the limiter described in Patent Document 1 is attached to the needle hub of an injection device, it is possible to suction the drug from a vial with the injection device. Also, if it is before the sticking adjustment tool for an injection needle described in Patent Document 2 is attached to an injection device, it is possible to suction the drug from a vial with the injection device.    Patent Document 1: Japanese Unexamined Patent Application Publication No. 2001-137343    Patent Document 2: Japanese Unexamined Patent Application Publication No. 2000-37456